Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$237.36	11.270%	$264.1105	$264.11	$264.10	$264.10
Purchase #2	$107.51	5.399%	$113.3145	$113.31	$113.30	$113.30
Purchase #3	$109.45	13.261%	$123.9642	$123.96	$123.95	$124.00
Purchase #4	$48.41	13.565%	$54.9768	$54.98	$55.00	$55.00
Purchase #5	$115.53	13.803%	$131.4766	$131.48	$131.50	$131.50
Purchase #6	$106.25	11.675%	$118.6547	$118.65	$118.65	$118.70
Purchase #7	$36.35	13.153%	$41.1311	$41.13	$41.15	$41.10
7 purchase totals =	$760.86		$847.6284	$847.62	$847.65	$847.70